Absolute Pressure: The total of the indicated gage pressure plus the atmospheric pressure. The abbreviation is PSIA.

Absorption - The loss of power in an optical fiber, resulting from conversion of optical power into heat and caused principally by impurities, such as transition metals and hydroxyl ions, and also by exposure to nuclear radiation.

Acceleration: A change in velocity with respect to time

Accelerometer: A device which converts the effects of mechanical motion into an electrical signal that is proportional to the acceleration value of the motion.

Acceptance angle - The half-angle of the cone within which incident light is totally internally reflected by the fiber core. It is equal to arcsin (NA).

Active power - A power measurement that multiplies the voltage portion of the signal being measured by the current that is in phase with that voltage.
 

Analog output - A signal generated from a meter, for example, which can drive a recorder, an external display, or a controlling device such as a heater, motor, etc. Analog signals used for such purposes are typically 4-20mA , 1-5Vdc, or similar ranges.
 

Apparent Power - A term only applicable to Alternating Current (AC) circuits, it is the product of the voltage applied times the current flow. The unit of measure is VA, or Voltamperes.
 

Atmospheric Pressure: The pressure exerted upon the earth's surface by the air because of the gravitational pull of the earth. Standard atmosphere pressure at sea level is 14.7 pounds per square inch (psi).

Attenuation - A general term indicating a decrease in power from one point to another. In optical fibers, it is measured in decibels per kilometer at a specified wavelength.

Auto hold - The ability of a measuring device to wait until a reading has stabilized before holding (storing) that reading on the display.
 

Auto-ranging - Ability of a measuring device to automatically
select the appropriate range of measurement.

Bandwidth - The transmission capacity of a system.

Buffering - 1. A protective material extruded directly on the fiber coating to protect the fiber from the environment (tight buffering). 2. Extruding a tube around the coated fiber to allow isolation of the fiber from stresses on the cable (loose buffered).

Buffer Tubes - Loose-fitting covering over optical fibers used for protection and isolation.

Bundle - Many individual fibers contained within a single jacket or buffer tube. Also, a group of buffered fibers distinguished in some fashion from another group in the same cable core.

Cable Tester - A handheld electronic device that is used to measure the electrical and physical properties of network cabling. Used commonly to certify cabling to known standards, or as a troubleshooting tool.

Cladding - The outer concentric layer that surrounds the fiber core and has a lower index of refraction.
 

Coaxial Cable - A popular transmission medium usually consisting of one central wire conductor (two for twinaxial cable) surrounded by a dielectric insulator and encased in either a wire mesh or an extruded metal sheathing. Commonly used for Cable TV (CATV) or older computer networks.

Cold Junction Compensation - Circuit in a measuring device which resolves the difference between an ambient temperature reference (used when device was calibrated) and the actual operating temperature of the measuring device.
 

Conductance - The reciprocal of resistance expressed in term of Siemans (formally mhos)

Connector - A mechanical device used to provide a means for aligning, attaching, and achieving continuity between fibers.
 

Consolidation Point - A location for interconnection between horizontal cables that extend from building pathways and horizontal cables that extend into work area pathways.

Continuity beeper- Audible tone emitted from a meter when resistance measured falls below a threshold level (typically 20-50 Ohm).

Core - The central, light-carrying part of an optical fiber; it has an index of refraction higher than that of the surrounding cladding.
 

Cosine F - Voltage and Current sometimes do not happen together, often there is a difference. The difference is an angle, F, a value between 0 and 90. The greater the angle, the bigger the difference between True and Apparent Power, the smaller the Power Factor. If Voltage and Current happen at about the same time, F is small, the values of True and Apparent Power are close, Power Factor approaches 1.
 

Criterion Sound Level - The eight hour average weighted sound level, expressed in dB, that corresponds to the maximum permitted daily exposure to noise as prescribed in national and state regulations.

Cross-Connection - A connection scheme between cabling runs, subsystems, and equipment using patch cords or jumpers that attach to connecting hardware on each end.
 

Crosstalk - The unwanted transfer of energy (signal) from one circuit to another circuit. Crosstalk interferes with the desired data signal. Handheld cable testers can be used to determine the level of unwanted crosstalk in network cabling.

Data Acquisition - The ability of an instrument to communicate measurement information as it occurs. The meter must be in communication with a computer for measurement storage to occur.
 

Datalogging - The ability of a meter to store measurement information "on board" in nonvolatile memory until such time it can be downloaded to a computer for storage, analysis and report generation.
 

Data hold - Function of a measuring device which holds a displayed value when a user presses a key or button.
 

dB (Decibels) - The unit of measure used when measuring the level of sound. Every 3dB represents approximately double (-3dB = 1/2) the power or sound level, ie: 53dB is twice as loud as 50dB.

dB (Decibel) - In fiber optics, a standard logarithmic unit for the ratio of the power that was received over the power that was originally sent.
 

dBm - Decibels above one milliwatt. A measure of power equal to 10 times the common logarithm of the ratio of a given power to 0.001 watt

dBµ - Decibel referenced to a microwatt.

Detector - An optoelectronic transducer used in fiber optics for converting optical power to electric current. In fiber optics, usually a photodiode.
 

Differential - In dual input measuring devices, the differential is the displayed difference between the two inputs. (Input A - Input B = Differential).

Diffraction - The bending of radio, sound, or light waves around an object, barrier, or aperture edge.
 

Diode check - Function of a measuring device which analyzes the operation of a diode. The two leads of the diode are inserted into the device and the user is alerted visually and/or audibly as to the diode's integrity.

Dispersion - A general term for those phenomena that cause a broadening or spreading of light as it propagates through and optical fiber. The three types are modal, material, and waveguide.
 

Displacement - change of position, or distance, usually measured from mean position or position of rest. Usually applies to uniaxial, less often to angular motion.

Display counts - The number of display units a meter or other device can indicate. For example, a 3-1/2 digit display can indicate from 0 - 1,999 (which is 2000 counts); a 4-1/2 digit display can indicate from 0 - 19,999; a 3-3/4 digit display can indicate from 0 - 3,999 counts, etc. If a meter is "bi-polar" it can indicate positive and negative units depending on the polarity of the signal being monitored. For example ±1999.
 

Duty Cycle - The ratio of the working time to the total time of a pulse train expressed as a percent.
 

Elapsed Time - The period of time between the start of a measurement series to the last measurement observed or recorded.
 

Electric Power - is the rate at which electricity does work. More work done in a set time, or the same work done in a shorter time, both require more electrical power. The unit of measure for electric power is the Watt . Electric power, measured in Watts is also known as True Power.
 

Emissivity - A term related to temperature measurement using Infrared radiation. Errors in IR measurements can occur based on the color, shape and presence of reflection on the measurement surface. A wide emissivity adjustment should be available on an IR thermometer to allow the user to compensate for these types of errors.
 

EMF/Electromagnetic radiation - Waves generated by a magnet configuration which consists of a coil wound around a steel core. The core is strongly magnetized when current flows through the coil. Video monitors, power lines, and wire harnesses are a few devices which produce electromagnetic radiation.

Entrance Facility - An entrance to a building for both public and private network service cables including the entrance point at the building wall and continuing to the entrance room or space.
 

EMD (Equilibrium Mode Distribution) - The steady modal state of a multimode fiber in which the relative power distribution among modes is independent of fiber length.

Equipment Room - A centralized space for telecommunications equipment that serves the occupants of the building. Equipment housed herein is considered distinct from a telecommunications closet because of its nature or complexity of the equipment.

Exchange Rate - (also Doubling Rate) Refers to the rate in which sound energy is averaged over time. Every time the sound energy doubles, the measured level increases by 3dB ,which most of the world uses. In the U.S., OSHA uses a 5dB exchange rate.

Frequency - Of a periodic wave, the number of identical cycles per second. Usually expressed in Hertz.
 

Fresnel Reflection - The reflection that occurs at the planar junction of two materials having different refractive indices; Fresnel reflection is not a function of the angle of incidence.

g units or gravitational units - A way to express an acceleration, in terms of a ratio. Divide a given acceleration by the appropriate value (9.80665 m/s2 or 386.087 in/sec2 or 32.1739 ft/sec2).

GO/NO GO Alarm - An output from a meter or controller which is used to indicate when a preset measurement point has been reached or exceeded. The alarm may be visible, audible, electrical or any combination of these.

Graded-index Fiber - An optical fiber whose core has a nonuniform index of refraction. The core is composed of concentric rings of glass whose refractive indices decrease from the center axis. The purpose is to reduce modal dispersion and thereby increase fiber bandwidth.
 

HC (Horizontal Cross-Connect) - A cross-connect of horizontal cabling to other cabling, e.g., horizontal, backbone, equipment.

IC (Intermediate Cross-Connect) - A cross-connect between the main cross-connect and the horizontal cross- connect in backbone cabling.

Inches of WATER GAUGE or COLUMN (IN WG or IN WC) A unit of air pressure measurement equal to the pressure exerted by a column of water 1 inch high.

Index of Refraction - The ration of the velocity of light in free space to the velocity of light in a given material.

Interconnection - A connection scheme that provides for the direct connection of a cable to another cable or to an equipment cable without a patch cord or jumper.

Insertion Loss - The loss of power that results from inserting a component, such as a connector or splice, into a previously continuous path.

Kelvin Connection - A four wire method of connecting test leads which is designed to eliminate or greatly reduce the effect of lead or contact resistance and thus permitting accurate measurements of low resistance.

Laser - Light Amplification by Stimulated Emission of Radiation. A light source producing, through stimulated emission, coherent, near monochromatic light. Lasers in fiber optics are usually solid-state semiconductor types.
 

LCD - Acronym for Liquid Crystal Display. Liquid crystal is a liquid that is not isotropic, that is, it forms patterns when polarized. The orientation of the molecules of the liquid are arranged by the meter to form the display.
 

LED - Acronym for Light Emitting Diode, a very common display type. An electrical current is passed through the diode causing illumination aided by the colored lens which surrounds them. LEDs usually have 7 light segments per digit when used as an Alpha-numeric display. Also commonly used to indicate ON/OFF or status functions individually. Orange-red, green, and yellow are common LED colors.
 

Load - A device that is driven by the output of a meter or other measuring/controlling device. An example of a load is a resistor being measured by a multimeter. The resister "loads" the meter since it becomes part of the measuring circuit.

Local Area Network, LAN - A group of PCs, servers, printers and similar devices connected over a network in a relatively limited geography.

Main Cross-Connect - The cross-connect in the main equipment room for connecting entrance cables, backbone cables, and equipment cables.
 

Material Dispersion - Dispersion resulting from the different velocities of each wavelength in an optical fiber.

Microprocessor - Integrated circuits which perform many instructions per second (mathematical equations, calibration data storage, display updates, etc.) precisely and quickly. Microprocessors are at the heart of computer accuracy, repeatability, and speed, providing similar attributes to electronic measuring devices such as calibrators, multimeters, thermometers, etc.
 

Min/max - A function of a measuring device which records (saves) the highest and lowest reading it has encountered since being reset (cleared) or powered up.

Modal Dispersion - Dispersion resulting from the different transit lengths of different propagating modes in a multimode optical fiber.

Mode - A possible path followed by light rays.

Multimode Fiber - A type of optical fiber that supports more than one propagating mode.
 

Multiplexer - A device that sequences access to a communcation port. Several different devices can share a single COM port on a computer if they are multiplexed.

NA (Numeric Aperture) - The number that expresses the light-gathering ability of a fiber.
 

Noise Dose - A measure of the exposure to noise expressed as a percentage of a maximum permissible exposure. The maximum permissible exposure (or 100%) is prescribed in national or state regulations.

Network - A series of computers and related devices interconnected by common communications channels

OTDR (Optical Time Domain Reflectometry) - A method of evaluating optical fibers based on detecting backscattered (reflected) light. Used to measure fiber attenuation, evaluate splice and connector joints, and locate faults. Also, the equipment used to perform such measurements (Optical Time Domain Reflectometer).
 

Overload - A signal that is greater than that which a measuring device can accurately or safely accept. Many meters have overload protection in the form of a fuse, or similar device, to protect the meter from such a signal.
 

Over range indication - Visual display alerting the user that the signal present at the meter's input is out of range.
 

Peak hold - The ability of a measuring device to hold the highest reading until the user clears the display. Also known as Peak Detect.

Photodetector - An optoelectronic transducer, such as a PIN photodiode or avalanche photodiode.

Photodiode - A semiconductor diode that produces current in response to incident optical power and used as a detector in fiber optics.

Photon - A quantum of electromagnetic energy; a particle of light.
 

PSI ( POUNDS PER SQUARE INCH) a measure of pressure. One psi is equal to the pressure exerted by 2.31 feet of water column. exerted by 2.31 feet of water.

PSIA: Pounds per square inch absolute. Referenced to a vacuum.

PSID: Pounds per square inch differential. The pressure difference between two points.

PSIG (POUNDS PER SQUARE INCH): 0 psig = 14.696 psia (psi absolute) = 1.0 atmosphere.

Power Factor - is the ratio of Watts to VA, or True Power divided by Apparent Power. This can be expressed as a decimal or percentage, i.e.: PF=0.75 or PF=75%. True Power is never greater than Apparent Power, so the Power Factor is never greater than 1. Power Factor may also be expressed as Cosine F where F is an angle between 0 and 90.
 

Psychrometers (Wet Bulb) - A relative humidity measuring device which has two thermometers. One measures ambient temperature (dry bulb), the second measures the temperature of an element surrounded by a fibrous material saturated with water (wet bulb). Reference tables are then used to determine relative humidity.

Receiver - An electronic device which converts optical signals to electrical signals.
 

Resolution - The smallest value a display device can indicate. For example, if a device can display 0.0 to 100.0 RPM, the smallest measurement and, therefore, the resolution is 0.1 RPM.
 

Response time - The rate at which a measuring device responds to a change in the measured variable.

Responsivity - The ratio of a photodetector's electrical output to its optical input in an optical fiber.
 

RH Capacitance Probe - Capacitive device that senses relative humidity. The meter used with such a probe senses the change in capacitance based on the moisture encountered by the capacitor's dielectric and displays the relative humidity based on this capacitance value.
 

RH Resistance Probe - Resistive device that senses relative humidity. The meter used with such a device monitors the resistance of the probe which changes proportionately to th amount of moisture encountered. The meter then displays the relative humidity based on this resistive value.
 

RTD - A temperature measurement device whose resistance is proportional to temperature. 2,3, and 4 wire RTDs are available.

Single Mode Fiber - An optical fiber that supports only one mode of light propagation above the cutoff wavelength.
 

Single Phase - A good example of a single phase power source is a typical AC wall outlet. This is considered to be single phase because there is a single alternating voltage/current available. Three-phase on the other hand, provides three separate alternating signals.

Source - The light emitter, either an LED or laser diode, in a fiber optic link.

Spectral Width - A measure of the extent of a spectrum. For a source, the width of wavelengths contained in the output at one half of the wavelength of peak power. Typical spectral widths are 20 to 60 nm for an LED and 2 to 5 nm for a laser diode.

Splice - An interconnection method for joining the ends of two optical fibers in a permanent or semi-permanent fashion.

Step-Index Fiber - An optical fiber, either multimode or single mode, in which the core refractive index is uniform throughout so that a sharp step in refractive index occurs at the core-to-cladding interface. It usually refers to a multimode fiber.

TC (Telecommunications Closet) - An enclosed space for housing telecommunications equipment, cable terminations, and cross-connects. The closet is the recognized cross-connect between the backbone cable and horizontal cabling.
 

Thermistor - A resistive temperature measurement device whose resistance decreases as the temperature increases. A thermistor is a stable, compact, and rugged two terminal ceramic-like semiconductor bead.
 

Thermocouple - A 2-wire temperature measurement sensor constructed of two dissimilar metals which form a junction. Current flows from one metal to the other in proportion to temperature. A millivolt signal is then measured by a thermometer or other device to display temperature.
 

Threshold - (also cutoff) Sound levels below this point are excluded from dosimeter measurements. National and state regulations determine the threshold level. OSHA uses an 80dB level.

Tight Buffer - A cable construction where each fiber is tightly buffered by a protective thermoplastic coating to a diameter of 900µm.
 

Torque - The measure of the twisting force generated by an object.

Traffic - The volume of data transmitted over a LAN at any given time. Traffic is generated by the devices and associated software applications that are running on the network. Excessive traffic on a network can seriously impair performance of a LAN. The NETcat and NETcat Plus allow network managers to actively monitor 10 Base-T Ethernet network traffic to help them configure their networks for optimal performance

Transducer - A device that converts energy from one form to another. It normally applies to devices that convert physical measurements into electrical signals.

Transducer Vibration - A device that converts movement into electrical signals proportional to the amount of movement.

Transistor test - A function of a measuring device which can be used to check the operation of a transistor. The leads of a transistor are inserted into the meter which indicates whether the device is operational or defective.

Transmitter - An electronic package which converts an electrical signal to an optical signal.
 

True Power - Electric power, measured in Watts.
 

True RMS Voltmeter - A voltmeter that measure an AC sine wave (voltage and current) and displays the root mean square (rms) of each waveform cycle. Important when measuring true power.
 

Var or Voltampere-reactive - The product of Apparent Power times Sine F. This is the Reactive, or non-work producing, component of Apparent Power. Var = Apparent Power if F = 90 degrees, therefore Power Factor = 0 and True Power = 0.

Velocity - Rate of change of displacement with time

Vibration Meter- A device or detector that measures a signal from a vibration sensor. The display is usually shown in units of displacement, acceleration or velocity.

WA (Work Area) - A building space where the occupants interact with telecommunications terminal equipment; i.e. PCs, telephones, and other office equipment.
 

Watt - The unit of measure for electric power.

Wavelength - The distance between the same two points on adjacent waves; the time required for a wave to complete a single cycle.
 

Zero adjust - Ability of a meter to be calibrated to a null or "zero" reference ensuring accurate readings in all ranges.
 

© Extech Instruments Corporation